Good idea to make the LED have a DC source. The inverse voltage of an LED is very low ~5V, AC can really upset them. You don't want to exceed that voltage for any time.
Question about your KT88 orientation. The (Genalex) spec sheet says that pins 4 and 8 on the two tubes should be inline. In your experience if that not really important? Thanks!
In this case the hot part of the plates are angled away from each other and away from the other tubes. The MAIN thing IMHO is to not jam them next to each other like so many KT88 amps do.
Isn’t this basically the same power supply and transformer used in your EL34 amp? If so we would expect the voltage to droop further under the higher cathode bias current load of a KT-88 over an El34. I expected to see you use a 380 to 400 V CT transformer to have higher B+ than your El34 amp.
Hi Steph, thanks for letting us have a peek in the kitchen, so to say. You made a good point for grounding the secondary minus on the OPT. Regarding the choke orientation, I see you have rotated it 90 degrees to the power transformer. I have always been on the fence what is better. Since the ripple is in phase with the power transformer, stray magnetic field will not make it much worse, has always been my though. Thus I would prefer to have the choke rotated 90 degrees to the OPTs. But I would be interested to hear your thoughts about that. Also, the choice to use a power resister instead of a second (economy choke, something like 1H) is that based on listening experiences, that it does not matter. Or is it based on ripple measurements? Obviously a second choke is a pain in terms of integration and extra cost. And many designs use resisters. I always wondered how much is cost reduction and how much is empirical engineering? Also here, your inputs are valuable.
On the choke orientation: The distance from the output transformers and that the lines of stray inductance are not in line with them, makes all of that conjecture a moot point. Moving these components apart is more important IMHO. If the choke was next to the output transformer, if someone was trying to cram everything into a tiny chassis, I would test which was quieter and likely would go with an aluminum chassis. I tried it in both on this style amp and heard nothing. Given it made no difference, it's rotated this way for aesthetic reasons. And same on the second choke, years ago I build a pair of 6SQ7/EL34 amps, one with one stage of filtering using a single choke and a second using 2 chokes (the same first choke and a smaller second one) and there was no difference in the noise floor of the amp I could hear. I then started using a CLCRC as extra insurance over a simple CLC for folks with super sensitive speakers + the extra resistance before the larger 220uf cap is easier on the rectifier tube when space is limited under the chassis. Note the original "Blue glow" amp that thousands of people have built has a single choke CLC filer.
I noticed that your ventilation holes for the KT88s look a bit oblong (not really round). I found that using the step drill (Christmas tree) bits make a perfect round hole in thinner sheet metal. The regular twist drills tend to make out of round holes in thin material. Just a thought.... 🙂
Please be patient. I know everyone expects these project videos to proceed uninterrupted but I have multiple projects going on at the same time, sometimes am waiting on parts or simply the time to work on a specific one you may be interested in. I'll get back on that when I can.
I built that amp and it is quite and has plenty of base. I am using a 7 tube pre-amp to drive it. You should use higher watt cathode resistors so they run cooler. The resistor in the power supply needs to be closer to the caps, there is to much wire with high voltage.
Awwwww, doggie is sooo sleepy, but still listening and watching you with one eye open. ☺
Well she isn't listening, she is deaf but she does keep an eye on me :) I swear she sleeps like 20 hours a day lol
Thanks for starting a different amp build. I working on the color preamp now and appreciate your channel.
Very pure design 👍: "Form Follows Function", without "chichi"!
Looks like a great design so far. Very smart running wires from the negative speaker binding posts to the star ground as well.
Good idea to make the LED have a DC source. The inverse voltage of an LED is very low ~5V, AC can really upset them. You don't want to exceed that voltage for any time.
That looks perfect
Click Like before watching the video. :)
I like how clean your amps look. How did you drill the vent holes around the KT88 sockets. The chassis looks great!
Eyeballed the layout on some paper, center punched and drilled.
@@SkunkieDesignsElectronics That is very nicely done. I have tried that before and always seem to have issues with the alignment.
Question about your KT88 orientation. The (Genalex) spec sheet says that pins 4 and 8 on the two tubes should be inline. In your experience if that not really important? Thanks!
In this case the hot part of the plates are angled away from each other and away from the other tubes. The MAIN thing IMHO is to not jam them next to each other like so many KT88 amps do.
Isn’t this basically the same power supply and transformer used in your EL34 amp? If so we would expect the voltage to droop further under the higher cathode bias current load of a KT-88 over an El34. I expected to see you use a 380 to 400 V CT transformer to have higher B+ than your El34 amp.
This is a higher voltage and ma rating transformer.
Hi Steph, thanks for letting us have a peek in the kitchen, so to say. You made a good point for grounding the secondary minus on the OPT. Regarding the choke orientation, I see you have rotated it 90 degrees to the power transformer. I have always been on the fence what is better. Since the ripple is in phase with the power transformer, stray magnetic field will not make it much worse, has always been my though. Thus I would prefer to have the choke rotated 90 degrees to the OPTs. But I would be interested to hear your thoughts about that. Also, the choice to use a power resister instead of a second (economy choke, something like 1H) is that based on listening experiences, that it does not matter. Or is it based on ripple measurements? Obviously a second choke is a pain in terms of integration and extra cost. And many designs use resisters. I always wondered how much is cost reduction and how much is empirical engineering? Also here, your inputs are valuable.
On the choke orientation: The distance from the output transformers and that the lines of stray inductance are not in line with them, makes all of that conjecture a moot point. Moving these components apart is more important IMHO. If the choke was next to the output transformer, if someone was trying to cram everything into a tiny chassis, I would test which was quieter and likely would go with an aluminum chassis. I tried it in both on this style amp and heard nothing. Given it made no difference, it's rotated this way for aesthetic reasons.
And same on the second choke, years ago I build a pair of 6SQ7/EL34 amps, one with one stage of filtering using a single choke and a second using 2 chokes (the same first choke and a smaller second one) and there was no difference in the noise floor of the amp I could hear. I then started using a CLCRC as extra insurance over a simple CLC for folks with super sensitive speakers + the extra resistance before the larger 220uf cap is easier on the rectifier tube when space is limited under the chassis. Note the original "Blue glow" amp that thousands of people have built has a single choke CLC filer.
I noticed that your ventilation holes for the KT88s look a bit oblong (not really round). I found that using the step drill (Christmas tree) bits make a perfect round hole in thinner sheet metal. The regular twist drills tend to make out of round holes in thin material. Just a thought.... 🙂
I made them that shape on purpose :)
What about 6c33c. Any progress?
Please be patient. I know everyone expects these project videos to proceed uninterrupted but I have multiple projects going on at the same time, sometimes am waiting on parts or simply the time to work on a specific one you may be interested in. I'll get back on that when I can.
I built that amp and it is quite and has plenty of base. I am using a 7 tube pre-amp to drive it. You should use higher watt cathode resistors so they run cooler. The resistor in the power supply needs to be closer to the caps, there is to much wire with high voltage.
They will still dissipate the same amount of heat. 3.3W of heat is 3.3W of heat. 10W is 3X the power so will work fine.
👍♥️🫂